1. Field of the Invention
The present invention relates to a producing method of a wired circuit board and, more particularly, to a producing method of a wired circuit board such as a chip on film (COF) board.
2. Description of the Related Art
Conventionally, an additive method has been used in the formation of a conductive pattern for a wired circuit board such as a COF board. For example, it is proposed that a conductive pattern made of copper is formed by the additive method on an insulating base layer made of polyimide which is formed on a metal supporting layer made of stainless steel (see, e.g., Japanese Unexamined Patent Publication No. 2006-332549).
That is, in Japanese Unexamined Patent Publication No. 2006-332549 mentioned above, a conductive thin film is formed on the upper surface of the insulating base layer, and then the conductive thin film is covered with a negative dry film resist. The negative dry film resist is exposed to light from thereabove via a photomask and then developed to form a plating resist in a pattern reverse to a wired circuit pattern. It is subsequently proposed that the conductive pattern is formed on the surface of the conductive thin film exposed from the plating resist through the precipitation of copper by electrolytic copper plating.